1. Field of the Invention
The invention relates to a longitudinal measuring instrument, preferably with digital path coverage, which is constructed according to the Abbe principle. As is known in the art, the Abbe principle requires that a path to be measured be the rectilinear continuation of the graduation of the measuring instrument. In this manner measuring errors of the first order are avoided which may have been caused, for example, by the displacement of a movable member from its guides.
2. Description of the Prior Art
Longitudinal measuring instruments designed according to the Abbe principle are already known, for example, from West German Auslegeschrift No. 1 237 334. The apparatus disclosed in that Auslegeschrift has a measuring spindle sleeve which is slidingly positioned in rollers with a glass scale built into its axis. In order to read the scale, a stationary optical reading instrument is mounted at a housing of the longitudinal measuring instrument. This arrangement of the prior art requires a large overall length for the measuring instrument.